Dangerous abstractions

Abstraction is "the process of taking away or removing characteristics from something in order to reduce it to a set of essential characteristics."
As developers, we use abstractions all the time.
To say something:

• using Maven to abstract the complex process of getting parts that conforms our application + compilation process (among others).

• using a proxy class that takes responsibility of certain aspects of our application.

• creating bash scripts to automate repetitive tasks.

Abstractions are the best way to deal with complexity.
But, as mentioned in the Law of Leaky Abstractions (http://www.joelonsoftware.com/articles/LeakyAbstractions.html)
"...(Abstractions) save us time working, but they don't save us time learning.". Even if you know how an abstraction works, take your time to learn what it is doing behind the scenes.

Well, to be honest, sadly, that's not always possible. GWT (https://developers.google.com/web-toolkit/) is a good example. It magically converts/permutes Java code, to Javascript code. The main objective of GWT abstraction is to hide Javascript code. Just use the language that you already know, Java. To be honest, the idea makes sense. In fact, GWT is just another framework that allows compilation/permutation from one language to the other: Clojure, Groovy, Coffescript, etc. 1 The truth is that we have no access (or it would be terribly complex to access to) the mechanism that transforms input to target code. That kind of abstractions are a little bit dangerous. What happen if something fails during the process? Trying to do a workaround on such heavy abstractions is, at least, harmful.
The truth is that sometimes we have to rely on this kind of powerful abstractions. JVM creating bytecode is a huge one, in example, and nobody will even try to find an alternative to that.
So we have to be careful when picking the abstractions we are going to use.
To comprehend risks of relying on things out of our control, or even worst, of our understanding.

1. The process is not exactly the same, in fact. GWT permutes Java code to Javascript. Clojure and Groovy compiles code to Java Bytecode. Coffescript provides "syntatic sugar".